Radio navigation system



oct- 17 1950 s. w. sEELEY 2,526,287

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m10 NAVIGATION SYSTEM 7 Sheets-Sheet 5 Filed Dec. 29, 1945 Oct. 17, 1950s. w. sl-:ELl-:Y 2,526,287

RADIO NAVIGATION SYSTEM Filed Dec. 29, 1945 7 Sheets-Sheet 4 MAF/ffl?Pl/L ff P/P I 41E-jl /lvPur 3 v I f (ayaxe) I N VEN TOR.

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Oct. 17, 1950 s. w. sEELEY amo mvmmon SYSTEM wm 9 2 mm .M D Il .m vm i FPatented Oct. 17, 1950y RADIO NAVIGATION SYSTEM Stuart W. Seeley, RoslynHeights, N; Y., assignor to Radio Corporation of America, a corporationof Delaware Application December 29, 1945, Serial No. 638,387

My invention relates to position determining systems and moreparticularly to pulse-echo radio systems of the type that transmit radiopulses from an aircraft, a ship or the like to a pair of repeating orreflecting ground stations, and then receive said pulses from the groundstations to determine the distances to the two ground stations. Thus,the position of the transmitter carrying craft may be determined fromthe two pulse-echo determined distances and from the known positions ofthe two ground stations.

The present invention is an improvement over the system described in mycopending application Serial No. 381,020, led February 28, 1941, andentitled Position Determining Systems, now Patent No. 2,405,239. Onespecific use for. the system described hereinafter is for blind bombingof a target. In addition to determining the position of the bombcarrying aircraft, my improved system also gives the rate at which theaircraft is moving away from one of the ground stations (referred to asthe rate station) ,and this rate information may be fed into a bombingcomputer. f'

An object of the invention is to provide an improved method of and meansfor determining the position of a craft or other mobile unit.

Another object of the invention is to provide an improved method of andmeans for bombing a target that is not visible.

Another object of the invention is to provide an improved method of andmeans for determining the rate at which a craft or other mobile unit ismoving away from or toward a ground station.

Still another object of the invention is to provide an improved methodof and means for producing marker and pulse indications in a positiondetermining system of the above-mentioned type.

Other objects, features and advantages of the invention will be apparentfrom the Ifollowing description taken in connection with theaccompanying drawing in which Figures 1a and 1b, which are to be placedside by side, are a block diagram of a position determining systemembodying the invention,

Figure 2 is a circuit diagram of the quadrature networks and goniometerphase shifters shown in Fig. la.

Figure 3 is a view illustrating the marker and ground station pulses asthey appear on the end of the cathode ray indicator tube shown in Fig.lb,

Figure 4 is a group of graphs illustrating the selection of thetransmitted pulses.

24 claims. (ci. 343-15) lshifter as explained hereinafter.

Figure 5 is a circuit diagram of a pulse selecting circuit,

Figure 6 is a. group of graphs illustrating the selection of the markerpulses,.

Figures 7, 8 and 9 are groups of graphs that are referred to inexplaining the operation of the system when the indicator is switched tothe range positions for miles, 10 miles and 1 mile,

respectively,

Figure 10 is a diagram that is referred to in explaining a method ofoperation for/preventing station interference,

Figure 11` is a diagrammatic showing of a portion of a computerillustrating how it may be combined with the system shown in Figs. laand 1b, and

Figure l2 is a view of a differential unit that may be employed in theapparatus of Fig. v11.

In the several figures, similar parts are indicated by similar referencecharacters.

The operation of the system shown in Figs. `1a and 1b .is the same inprinciple as that of the system described in my above-identified pendingapplication. This principle is vas follows, assuming that the system isto be used for bombing a certain target: The rate pulses transmittedfrom the aircraft to the rate ground station are delayed with respect toa marker pulse before being radiated by an amount such that when eachrate pulse returns to the aircraft it coincides with a marker pulse. The drift pulses are transmitted similarly to the drift ground station.In said pending application the system is operated so that thiscoincidence of pulses occurs at the instant the target is reached, thecorrect pulse delay being preset and remaining unchanged during abombing run. y

According to the present invention the rate pulse delay Iis changedcontinuously during a bombing run lto maintain coincidence of the ratepulse and the marker ypulse indications on the indicator tube screen.'I'his continuously changing delay of the rate pulse is obtained bycontinuously rotating a phase shifting device which, as describedhereinafter, comprises three goniometer phase Shifters which areygeared. to each other by gears having a l0 to' 1 ratio. The instant thatthe target'is reached may be determined by means of a mileage countergeared to a phase shifter shaft. However, for bombing it is preferred.to couple a computer to the phase It will be evident that the rate ofmovement of the aircraft from the rate station is given by the rate of-rotation of the phase shifter shaft so long as the rate pulse andmarker pulse coincidence is maintained.

Referring to Figs. 1a and 1b, both the transmitted pulses and the markerpulses are derived from a crystal controlled oscillator I operating at93 kilocycles per second. The 93 kc. sine wave output of oscillator I0has its frequency divided by 10 by a frequency divider II to obtain a9.3 kc. sine wave signal. The 9.3 kc. signal has its frequency dividedby 10 by a frequency divider I2 to obtain a 0.93 kc. sine wave signal.

Rate pulse phase shift and selection The outputs of the frequencydividers I6, II and i2 are supplied over conductors I3, I4 and I6 toquadrature networks I1, I3 and I9, respectively. The networks I1, I3 andI3 supply 93 kc., 9.3 kc. and 0.93 kc. signals in quadrature relationover conductors 2|, '22 and 23 to goniometer type phase shifters 24, 26and 21, respectively, which function to delay the transmitted ratepulse.

The 93 kc. output of phase shifter 24 is supplied through conductors 9,a cathode follower tube 28 and a conductor 25 to a pulse selectorcircuit 29. The 9.3 kc. and 0.93 kc. outputs of phase shifters 26 and 21are supplied through conductors I6 and 20 and pulse shaping circuits 3|and 32, respectively, and over conductors 30 and 36 to the pulseselector circuit 29. In this way, as described more fully below, a halfcycle or fractional portion of the 93 kc. wave is selected periodicallyto produce an output pulse at output lead 40 of the pulse selector 29that recurs at the rate of 0.93 kc. per second. This selected pulse ispassed through a pulse shaper 33 to obtain a rate pulse of the properwidth for modulating the radio transmitter 34. The pulse from theshaping circuit 33 is supplied periodically through a switch 36 and anamplifier 31 to the transmitter 34.

Fig; 4 illustrates the method of pulse selection which is similar tothat describedV and claimed in my above-identied application. Theoutputs of the cathode follower 28 and the pulse shapers 3| and 32 areshown by the graphs 38, 39 and 4|, respectively, in Fig 4. It will beseen that graphs 39 and 4I represent pulses recurring at 9.3 kc. and0.93 kc. per second. To obtain the pulses 39 and 4'I, the pulse shapingcircuits 3| and 32 may each comprise a. limiter tube followed first by adifferentiating circuit and then by a clipping circuit. Such waveshaping circuits are so Well known in the art that they need not bedescribed in detail.

Fig. shows one suitable pulse selector circuit which comprises amulti-grid vacuum tube 42 having potentials of such value applied tothree of the grids that signal must be applied to all three grids beforethe tube passes anode current. Therefore, a half cycle of the 93 kc.signal is passed by the pulse selector 29 each time there is coincidenceof the 9.3 kc. pulses 39, the 0.93 kc. pulses 4I and said 93 kc. halfcycles. In the example illustrated, the negative biases on the grids areobtained by the well known grid leak biasing action, the grids beingdriven positive by the applied signals whereby there is a periodic flowof grid current. However, the grid biases may be obtained from batteriesor voltage dividers, if preferred.

The quadrature networks and the phase shifters shown in Fig. 1a and Fig.2 are designed the same as those described and claimed in my 4 copendingapplications Serial No. 548,183, now Patent No. 2,450,616, issuedOctober 5, 1948, tiled August 5, 1944, and Serial No. 547,255. nowPatent No. 2,496,920, issued February 7, 1950, filed July 29, 1944,respectively, and entitled, respectively, Electrical Networks for PhaseShifters" and Phase Shifters." This portion of the system will bedescribed in some detaill hereinafter.

Drift pulse phase shift and selection Reference will now be made to thephase shifters and the pulse selector for obtaining the drift pulse fortransmission to the drift ground station. It will be understood that therate and drift pulses are transmitted alternately atdifferent carrierfrequencies such as frequencies fI and f2, the switch 36 being operatedto engage its upper and lower contact points alternately for thispurpose. A switch 4'0 at the transmitter 34 is operated in synchronismwith the switch 36 for changing the carrier wave frequency.

The quadrature networks I1, I8 and I9 supply 93 kc., 9.3 kc. and 0.93kc. sine wave signals in quadrature relation over conductors 5|, 52' and53 to the goniometer type phase shifters 64, 66 and 61, respectively.The 93 kc. output of phase shifter 64 is supplied through conductors 68,a cathode follower tube 69 and a conductor 6I to a pulse selectorcircuit 62 that is similar tn the pulse selector 29.

The 9.3 kc. and 0.93 kc. signals from the phase shifters 56 and 51 aresupplied, respectively, to the pulse selector 62 through conductors 83,a pulse shaper 64 and a conductor 66, and through conductors 61, a pulseshaper 38 and a conductor 69. Thus, a drift station pulse recurring at arepetition rate of 0.93 kc. per second is obtained at the output lead 1|of the pulse selector 62 in the same way that the rate station pulse isobtained at the lead 40. The drift pulse is made of the desired width bya pulse Shaper 12 and supplied to the lower contact point of the switch36 for periodically pulse modulating the radio transmitter 34.

Phase shifter gearing The three phase shifters 24, 26 and 21 for therate pulse delay and selection are geared to each other with 10 to 1gear ratios so that the rotorof the phase shifter 24 makes 100 rotationsfor every 10 rotations of the rotor of phase shifter 26 and for every 1rotation of the phaseV shifter 21. These gear ratios correspond t-o theratios of the frequencies of the signals applied to the phase shifters.

As illustrated in Fig. la, the rotors of the phase shifters 24, 28 and21 may be rotated by turning a crank 13. The phase shifter 24 is driventhrough the gears 14 and 16, and 'I1 and 18. The phase shifter 26 isdriven through the l to 10 ratio gears 19 and 8|, and the 1 to 1 ratiogears 92 and 83. The phase shifter 21 is driven through the 1 to 10ratio gears 19 and 8| and through the 1 to 10 ratio gears 84' and 86.

A mileage counter 81 which is connected by bevel gears 88 to the phaseshifters indicates the mileage in units, tenths and hundredths.

For more rapid initial setting of the geared phase shifters, meanscomprising a knob 89 and a detent 9| are provided for rotating the phaseshifter 21 Without rotating the other phase shifters 26 and 24. Only thephase shifter 21 is rotated by the knob 89 when the knob is pulled awayfrom the panel 92 since this dis-l The quadrature networks Referring toFigureA 2, two resistive elements |0I, |03 and two reactive elements|05, |01 are connected to form a Wheatstone bridge. The resistiveelements |0|, |03 are in opposite arms of the bridge as are the reactiveelements |05, |01. A second Wheatstone bridge is formed with similarresistive arms |09, |`|I and similar reactive arms |I3, ||1. As in thecase of the iirst bridge, the resistive arms |09, III are opposed asarethe reactive arms II'3, I|1 and the four reactive elements are ofsimilar sign. The two bridges are connected in series by forming acommon connection I|9 at the junction of the arms |03, |01 of the firstbridge andthe junction of the arms |09, ||3 of the second bridge. Theinput terminals of -the two bridges are supplied from the conductors I3.

The rst output terminals |21 and |29 of the network are formed by thejunction of arms l0| and |01 and by the junction ci the arms |03 and |05of the first bridge.- The other pair of output terminals |3I, |33 areformed. by the .junction of the arms |09 and |'|1 and by the junction ofthe arms III and ||3 of the second bridge. These four terminals |21,|29, |3I, |33 become the source of quadrature phase currents which maybe applied for any desired purpose. In the present system, two of thefield coils |35, |31 of the goniometer phase shifter 24 are con nectedacross the terminals I21-I3I and |21- |29, respectively. The eld coils|4||43 of the goniometer phase shifter 54 are yconnected across theterminals |29--I33 and |33|3|, respectively. The rotor of the rstgoniometer is represented as a pick-up coil |41 while the rotor of thesecond goniometer is represented as a pick-up coil |49. 'I'he pick-upcoils each represent sources of voltage having a phase which may beadjusted through any desired angular shift up to 360 degrees percomplete rotation oi the pick-up coil. i v

To provide the best results the impedance of all arms of the two bridgesshould be made numerically equal. By way of example, where the signalfrom leads I3 has a frequency of 93 kilocycles, the several resistiveelements |0I, |03, |09 and may be 855 ohms whilel the several reactiveelements |05, |01, |I3 and |'|1 may have capacities of 2000micro-microfarads. These capacities at 93 kilocycles have a reactance ofapproximately 855 ohms. If the two bridges are thus arranged, it can beshown mathematically that the currents in the several output connections|21-|29, I29-I33, |33|3|', and |3I`|21 will be in quadrature with eachother and will continue to be in quadrature substantially independent ofthe resistances or impedances connected across the output terminalsprovided only that those resistances or impedances remain equal to eachother. f i

If the network is connected to pairs of goniometers whose inductivereactance is numerically equal to the impedance oi the other arms asshown in Figure 2, the phasey of the goniometer primary currents will becompletely independent of ambient temperature changes. This is lanimportant feature of the network in view of the fact that the goniometereld coils (usually wound of copper wire) have a substantial amount ofresistance. Since an ordinary goniometerv connection to a. conventionalphase shifter would be inuenced by the eilect of temperature changes inthe goniometer coil, it follows that the symmetrical arrangement-of thepresent network offers great'advantages. Likewise, if the inductance ofeach of the windings is made equal in ohms to each of the eight arms ofthe 4electrical bridge network, the phases oi' the currents through thegoniometer field coils o r stators |31, etc. maintain xed relations tothe phase lof the driving voltage from the leads |3 in the presence ofwide variations of ambient temperature. f

The goniometer eld coils |35, |31, I'4I and |43 have connected in serieswith them resistors |5I, |52, |53 and |54, respectively, these resistorsbe-A ing of like value.

The quadrature networks I8 and I9 which are supplied with 9.3 kc. and0.93 kc. signals from the leads I4 and I6, respectively, are the same asthe network I1 except for the fact that the circuit constants arediiferent so as to conform to the frequencies of the applied signals.However, in network I8 an additional resistor |56 of 100,000 ohmsresistance is included for supplying a 9.3 kc. signal adjustable inphase over a conductor |55, and in network I9 additional resistors |51and |58 of 500,000 ohms each are included for supplying 0.93 kc. signalsadjustable in phase over conductors |59 andV |6|,'respectively.

Circular cathode ray sweep In Fig. 1b the cathode ray indicator tube isshown at |62. A circular sweep of the cathode ray is obtained byapplying voltages in quadrature from amplifiers |63 and |64 to two pairsof deecting plates |66 and |61, respectively. A radial deflectingelectrode |66 has the received rate anddrift pulses and the markerpulses applied thereto from a conductor |65 so that they appear on thescreen |60 of the tube |62 als shown in Fig. 3 when the three pulses arein coincidence at their leading edges. It will be noted/ithat thepolarity of the drift pulse is reversedwith respect to the rate andmarker pulses. tube |62 is provided with a cathode |69, a, control grid|1| and the usual .anode electrodes (not shown) Sine wave voltages inquadrature are supplied to the input leads |12 and |13 of the ampliiiersI 53 and |64, respectively, by way of al pair of witches |14 and |16.Each switch has three positions which are shown as positions UI, II andIII-and which correspond to the mile scale, the 10 mile scale 'and theplmile scale on th indicator tube screen |60.

The indicatorcircular sweep are taken off resistors in series with thegoniometer stator coils.

Production of marker pulses The marker pulse selection is similar to thepreviously described rate and drift pulse selection, the principaldifference being that the goniometer type phase shifters are notemployed. Instead, except for a zero phase adjustment, the necessaryphase adjustments are made at the quadrature networks I8 and I9.

Referring to Figs. 1a and 1b, sine wave signal of 93 kc. is suppliedfrom the crystal oscillator I over a conductor |86 and through a zeroset phase shifter |81 to a marker pulse selector |88 (Fig, lb). Thephase shifter |81 is a resistorcapacitor network. The marker pulseselector |88 may be the same as the rate pulse selector 29.

Sine wave signal of 9.3 kc. is supplied from the quadrature network I8over a conductor |55 to a pulse Shaper |89, a suitable phase adjustmentbeing provided as indicated by the block |9| (Fig. 1b) As shown in Fig.2, the phase adjusting device |9| may be the resistor |56 provided inthe network I8 and having an adjustable tap thereon. The output of theshaper |89 is a rectangular pulse of microseconds duration, indicated at2, which recurs at the 9.3 kc. repetition rate. This pulse is suppliedto the pulse selector |88.

Sine wave signal of 0.93 kc. is supplied from the quadrature network I9over a, conductor |59 to a pulse Shaper |92, a suitable phase adjustmentbeing provided as indicated by the block |93. As shown in Fig. 2, thephase adjusting device |93 may be the resistor |51 provided in thenetwork I9 and having an adjustable tap thereon. The output of theshaper |92 is a rectangular pulse of 100 microseconds duration,indicated at 3, which recurs at the 0.93 repetition rate. This pulse issupplied to the pulse selector |88 through a switch SI when it is in theNo. I or 100 mile scale position. It may be noted that all switcheswhich are indicated in the drawing as having switch positions I, II andIII are preferably ganged for operation from a single knob.

Fig. 6 shows the time relation of the signals applied to the pulseselector |88 for the different switch positions. It will be seen that inthe No. I position a half cycle portion of the 93 kc. wave. indicated atI, is selected by the pulses 2 and 3 to produce a marker pulse 5 thatrecurs at the 0.93 kc. repetition rate. In the example illustrated, thepulse 5 has been narrowed by a differentiating transformer or circuit|94 (Fig. 1b). The regular marker pulses 5 and the offset marker pulsesdescribed hereinafter are supplied from the pulse selector |88 throughthe differentiating circuit |94 to a marker pulse amplifier |95, andfrom amplifier |95 over a conductor |65 to the radial deflectingelectrode |68.

In switch positions II and III the marker pulse 5'is not produced butinstead an offset marker pulse 6 is produced for a reason explainedhereinafter. With the switch SI in either position II or III arectangular pulse 4 of 100 microseconds duration is supplied to thepulse selector |88 in place of the pulse 3.

The pulse 4 is obtained by supplying sine Wave signal of 0.93 kc. fromthe quadrature network I9 over a conductor |6| to a pulse Shaper |96, aphase shift adjustment being provided as indicated by the block |91. Assho-wn in Fig. 2, the phase shifting device |91 may be the resistor |588 provided in the network I9 and having an adjustable tap thereon.

Referring again to the graphs of Fig. 6, it will be seen that in switchpositions II and III the rectangular pulses 2 and 4 select a, half cycleportion ofthe 93 kc. wave to produce the marker pulse 6 which is offset"with respect to the timing of the regular marker pulse 5, that is, itoccurs 107.5 microseconds later. Thus, the marker pulse 5 occurs 10circular sweeps later than the marker pulse 5 when the 1 mile scale(position III) is being used and 1 circular sweep later than the markerpulse 5 when the 10 mile scale (position II) is being used.

Reason for oset marker pulsev not of much importance for the mile scale(position I) as only a rough adjustment` of coincidence is required.Therefore, the regular marker pulse 5 is utilized in position I.

For the 10 mile and 1 mile scales, however, separate marker and ratepulse indications must appear on the indicator tube screen |60 as shownin Fig. 3. The use of the offset marker pulse 6 makes this possibleIbecause, as shown by the graphs in Figs. 8 and 9, the rate pulse 'I'RIand the offset marker pulse 6 do not occur simultaneously. Yet, thepulses TRI and 6 have the same time relation with respect to thecircular sweep of the cathode ray and are viewed simultaneously by theoperator due to persistence of phosphorescence of the screen orpersistence of vision or both.

Circle blanking In the 10 mile and 1 mile scale positions (positions IIand III) the cathode ray makes 10 and 100 circular sweeps, respectively,on the screen |60 per marker pulse unless the ray is blanked during someof the sweeps. Such blankingI referred to as circle blanking. isprovidedfor .positions II and III as otherwise the circular trace would be toobright as compared with the marker indication or pip. Circleblanking forthe 100 mile scale is unnecessary as there is only one circular sweepper marker pulse, this fact being illustratedin Fig. '1.

The graphs of Fig. 8 show how circle blanking is applied for the 10 milerange. First, it should be noted that, in practice, the cathode-ray tube|62 isbiased beyond beam current cut-off so that the cathode ray doesnot strike the screen |60 unless a positive pulse is being applied tothe grid I1I by way of a conductor 20|. Thus, the positive pulses 3 and4 which, for position II, are fed into the blanking circuit for circleblanking control are referred to as circle lighting pulses. The biasingsource as well as a conventional directcurrent setter circuit orbrightness equalizer circuit are represented by a block `202. As shownin Fig. 8, the pulse 3 occurs during the occurrence of the firstcircular sweep and during the occurrence of the rate and drift pulsesTRI and TDI, respectively. The pulse 4 occurs during the second circularsweep and during the occurrence of 9 the oiset marker pulse 6. In thisswitch position II the regular marker pulse is not produced.

Referring now to Fig. 1b and assuming the switches SI, S2, etc. are inthe No. II position, it will be seen that the pulse 3 is supplied over aconductor 203 and through the switch S2 to a circle-lighting pulseselector 204 and that the pulse 4 is supplied over a conductor 206 andthrough the switch S4 to a second circle-lighting pulse selector 201.The pulse selectors 204 and 201 are similar to the rate pulse selector20 except that each selector tube has only two grids, that have signalapplied thereto. In position II, each of the selectors 200 and 201 hasone of these two grids grounded by way of the switch S3. The biasadjustments are such that under these conditions the pulses 3 and 4 passthrough selectors 204 and 201, respectively, and are supplied to anamplier 208. The amplied circle-lighting pulses are supplied from theamplifier 208 over conductors 209 and 20| to the grid |1| of theindicator tube. Thus, the pulses 3 and 4 light up two successivecircular sweeps for the mile scale as illustrated in Fig. 8.

Assuming next that the switches Sl, S2, etc. are in the No. III or 1mile scale position, the pulses 2 of 10 microseconds duration aresupplied through a conductor 2 and the switch S3 to the pulse selector205. At the same time thepulse 3 is supplied through the conductor 203and the switch S2 to the pulse selector 204. The time relation of thepulses is shown in Fig. 9 where the first occurring pulse 2 is identiedas 2a. Thus the pulse 2a is supplied as a circle-lighting pulse to theamplifier 200.

Similarly, the pulse 2 is supplied through the conductor 2l I, theswitch S3 and a conductor 2 l2 to the pulse selector 201. The pulse 4 issupplied through the conductor 206 and the switch S4 to the pulseselector 201. Thus, as shown in Fig. 9, the second occurring pulse 2indicated at 2b is supplied as a circle-lighting pulse to the ampliiler208. It will be evident from an inspection of the graphs in Fig. 9 thatthe pulse 2a unblocks the cathode ray for one circular sweep during thetime the received rate and drift pulses TRI and 'I'DI are appearing onthe radial defiecting electrode |68 of the indicator tube. Also, thesecond occurring 10 ps. pulse 2b unblocks the cathode ray for onecircular sweep 107.5 microseconds or 10 circular sweeps later and duringthe time the offset marker pulsef6 appears on the electrode |68. Again,the regular marker .pulse 5 is not produced.

Since the offset marker pulse 6 is in the same time relation to thecircular sweep as the regular marker pulse 5 would beif produced, thedesired marker pulse indication or pip appears on the indicator screen|60 and, as in the case of-the 10 mile scale, this marker pulse pip andthe rate pulse indication or pip appear as separate and distinct marksas shown in Fig. 3 at the time the rate pulse is being adjusted to exactcoincidence with the marker pulse.

Reception of rate and drift pulses The rate pulses TRI, TR2, etc. andthe drift pulses TDI, TD2, etc. (Fig. 7), after retransmission from therate and drift ground stations, are received at the aircraft receiver2|3 (Fig. 1b) The rate and drift pulses are retransmitted from the rateand drift ground stations at the same carrier wave frequency. The rateand drift ground stations, for example, receive the aircraft transmitterrate and drift pulses on carrier-Wave frequencies fi and f2,respectively, andl both stations retransmit to the aircraft on afrequency f3.

The rate and drift pulses are supplied from the receiver 2|3 to 'a pulseinverter tube 2I4 and to a cathode follower tube 2I6. The outputs of thetubes 2|4 and 2|6 are supplied alternately through a switch 2|1, anamplier 2I8 and the conductor to the radial deflecting electrode |08 ofthe indicator tube |62.

The switch 2|1 is operated in synchronism with the transmitter switch 36(Fig. 1a) so that the cathode follower 2|6 supplies signal to amplifier2|8 when rate pulses are being transmitted to and retransmitted from therate ground station, and so that the pulse inverter 2|4 supplies signalto the amplifier 2|B when drift pulses are being transmitted to andretransmitted from the drift ground station. In this way the rate pulsepip is produced outward from the circular sweep and the drift pulse pipis produced inward `from the circular sweep as shown in Fig. 3.

Receiver blanlcing In the 10 mile and 1 mile scale positions II and III,respectively, noise signal from the receiver 2 i3 is prevented frompassing through the inverter and cathode followertubes'2l4 and 2|6during the occurrence of the offset marker pulses 6 so that there willbe no noise signal appearing on the radial deflecting electrode |68 toobscure or distort the marker pulse pip. This is accomplished byapplying blanking pulses to the screen f grids, for example, of theinverting and cathode follower tubes 2|4 and 2|6. The pulse 4 is usedTransmitter blanking At the aircraft, the transmitted rate and driftpulses will feed into the receiver 2|3 and appear on the indicatorscreen unless they are blanked out. They are blanked out by supplyingsome of the signal from the switch 36 (Fig. 1a) over a s conductor 222to an ampliler 223 (Fig. 1b). From the amplier 223 negative pulses aresupplied through a conductor 224, a switch 226 and the conductor 20| tothe grid of the indicator tube |62. The switch'226 may be opened toallow the transmitted pulses to appear on the -indicator screen |60 forchecking or Calibrating the equipment.

Scrambling circuit Rate and drift pulses retransmitted froml th rate anddrift ground stations due to triggering by other similarly equippedaircraft may be seenv on the cathode ray indicator tube |62 (Fig. 1b),and for that reason a Scrambler circuit is provided as indicated by theblock 221 in Fig. 1a for identifying the retransmittedrate and driftpulses due to triggering by the aircraft carrying the equipment of Figs.1a and 1b.

A positive voltage pulseis applied periodically tothe Scrambler circuit221 through a switch 228, and in response to each applied Vpositivepulse a negative voltage pulse of the proper timing and duration isapplied Ifrom the Scrambler circuit 221 to a grid of a frequency dividertubel (not shown) inthe frequency divider ll. The Scrambler circuitrepresented by the block 221 may be any suitable wave shaping means suchas a differentiating and clipping circuit for producing negative pulsesof the proper timing and width. The negative pulse from the circuit 221blocks the frequency divider tube momentarily and thus makes the dividerinoperative for a period during and immediately following said negativepulse.

Thus, the operation of the frequency divider stages and l2 is stoppedperiodically so that when normal operation of the dividers is resumedthe dividers will start with a phase relationship that is random withrespect to their previous output. As a result, the pulses due totriggering by other aircraft will not be stationary on the cathode raytrace but, instead, they will appear to be jumping around the cathoderay trace when either the 100 mile or 10 mile scale is being used.

On the l mile scale, the effect of scrambling is different because thestart of the timing sweep remains unchanged as it is produced directlyfrom the 93 kc. oscillator. However, the particular half cycle of the 93kc. wave that is selected by the puise selector is random. Consequently,it is not often that an interfering pulse will coincide with a sweepperiod that is unblanked.

The switches 228, 40 and 36 (Fig. 1a) and the switch 2|1 (Fig. 1b) areoperated in a fixed time relation by means of cams (not shown) which aredriven by a common shaft as indicated by the broken lines 229 associatedwith the switches.

Fig. shows the sequence of operation for rate and drift pulsetransmission and for scrambling It will be seen that at the end of eachpulse transmission period, the scrambling switch 228 is closedmomentarily to make the frequency dividers and I2 inoperative for aperiod equal to about one-half the pulse transmission period. Thecomplete switching cycle may take about 16 second, this making theduration of each scrambling period about V60 second.

The circle-lighting amplier 208 (Fig. 1b) has +B voltage removed fromits amplifier tubes for `a period substantially longer than the negativepulse from the Scrambler 221, specifically, for a period equal to thescrambling period so that no pips will appear on the indicator tubescreen |60 during the occurrence of the negative scrambling pulse orduring the short period immediately thereafter which is required for thefrequency dividers and I2 to resume normal operation. The short periodreferred to above falls within the to second scrambling period. The +Bvoltage is removed from amplifier 208 periodically by means of a camoperated switch 23| which is driven synchronously with the otherswitches operated from the shaft indicated at 229. Preferably, theduration of' the negative scrambling pulse is adjustable so that thescrambling may be changed by the operator if some interfering pulsesbegin to appear stationary on the cathode ray trace.

Combination with, computer When the equipment described in the foregoingpages i's employed for bombing a target, it preferably is used incombination with a computer. The portion of the computer that is ofinterest in the present case is shown diagrammatically in Fig. 11.

The computer includes a constant speed motor 236 which drives therate-pulse phase shifters 'through a variable speed drive 231 and aclutch 238. The clutch 238 is disengaged if the com- 1'2 puter is not tobe used with the position determining equipment.

The variable speed drive 231 is of conventional design comprising adriving disc 239, a ball carriage 24| and a cylinder 242. The speed atwhich the rate-pulse phase shifters are driven is adjustable by means ofa rack and pinion 243--244. The pinion may be rotated by a speedadjustment crank 246 so that the operator may adjust the rate ofrotation of the pulse-rate phaseshifter rotors to a rate that holds therate-pulse pip and the marker pulse pip coincident, as shown in Fig. 3,during a. bombing run. Thus, with these pips held coincident, the rateinformation is fed into the computer. The rate information is taken offthe shaft of the cylinder 242 by bevel gears 241 to drive the inputshaft of a differential unit .248 which may be of conventional designsuch as that shown in Fig. 12, for example.

The output shaft of the differential unit 248 drives the input shaft ofa second differential unit 249, the output shaft of which drives theinput shaft of a third differential unit 264. The out put shaft of unit264 drives a train of gears 25|, 252 and 253, each pair of gears havinga 10 to 1 ratio. The final gear of the train of gears carries a contactpoint 254 that makes contact with a contact member 256 after the finalgear has been rotated a, predetermined amount, and the bombs arereleased automatically in response thereto.

The differential unit 249 is provided so that the distance from ratestation to target may be preset into the computer before the aircrafttakes off on the bombing mission. 'I'his is done by turning a crank 251to run the contact point 254 back from its point of contact with member256. A mileage counter 258 driven by bevel gears 259 shows in units,tenths and hundredths the mileage that has been set into the computer.The differential unit 264 is provided so that the distance known astrail" distance may be cranked into the computer at the crank 262, thisdistance appearing on the counter 263.

The differential unit 248 is provided for the purpose of cranking rangeinto the computer. The position of the bomb release contact point 254 ischanged by way of the differential 248 whenever an adjustment is made inthe speed of rotation of the rate-pulse phase Shifters for maintainingpulse coincidence. This automatic adjustment is accomplished by couplingthe adjustment shaft of the differential unit 246 through a multiplierunit 26| to the speed adjustment crank 246. Since range is a product ofrate" and "time of fall, the time of fall is cranked into the computerfrom a crank 266 through a rack and pinion 26T-268 and through themultiplier 26| to the adjustment shaft of the differential 248. The"time of fall that is cranked in is shown in seconds on a counter 259.

It will be apparent that time of fall" of the bomb (which is a functionof altitude) and the rate (which is the speed at which the aircraft ismoving away from or toward the rate ground station) are multiplied inthe unit 26| to obtain range. It will also be apparent that while therate station pip and the marker pip are being held coincident, thecorrect value of rate is being set automatically into the multiplier26|.

'I'he multiplier unit 26| may be of any suitable type. In the exampleillustrated, it is designed the same as the variable speed drive 231.

Operation with computer First it should be noted that when'the ratepulse pip and the marker pip are aligned, the reading of the counter 81is the distance of the bomber from the rate ground station, the bomberreferred to being the one carrying the equipment being described.Actually, the counter 81-and the counter 258 read a maximum of mileswhich is more than the maximum length of a bombing run. Therefore, ifthe counter 81 is used to determine the full distance from the ratestation, the number of times it counts 10 miles must be noted as thebomber is own toward the target. In practice, the bomber is navigated byany suitable method to the point where the bomb The reading of thetarget distance counter 258 the distance from the rate station to thetarget, tins distance being set in before the bomber takes o on thebombing mission.

ffThe presetting of the computer prior to take oli for a bombing missionis done as follows:

(I) The bomb release contact point i254 is brought into contact with thecontact point 256, i. e., it is set to the bomb release position.

(II) Next the contact point 254 is run back by turning the crank 251until the target distance counter 258 reads distance from rate stationto target. The number of times the counter passes through the maximumreading of ten miles must be noted as the crank 251 is operated. It willbe understood that now if the crank 13 or the contact speed motor 236 isoperated so as to align the rate station pip and the marker pip, thetarget distance counter 258 will then read distance from the bomberitself to the target.

(III) 'I'he distance known as "trail is set in by means of the crank262, the trail distance counter 263 and a differential unit 264. Traills due to the air resistance presented to the bomb after its release andis the distance that the bomber would be past the target when the bombhit the target if the bomber continued its course. The trail distancemay be preset because the bombing is to be done while maintaining apredetermined air speed and altitude. Preferably, a windage correctionis included in the trail setting.

(IV) "Time of fall is set in by the crank 265 through the multiplier26|. This may be preset into the computer because the bomber is to bombfrom a predetermined altitude. The output of the multiplier gives therange which is the product of time of fall and .ratej the latter beingfed into the multiplier fduilingvlthe bombing run while the rate plsep"(ndfmarker pip are being held coincidentigg, y '1 f' Note is made of thefac t `the rate fed into the multiplier 26| depends-upon the angle o thebombing run with respect to the line from rate station to target. Thusthere is an automatic correction for this angle and no special settingor adjustment for it is required.

(V) 'I'he drift station phase Shifters are set by means of the crank 13and the knob 89 so that the drift station pip and the marker pip will becoincident at a predetermined bomb run distance from the drift groundstation. This distance appears on the counter 81.

The bombing run It will be understood that the course for av marker pip.He also holds the altitude and air speed at the predetermined values.

The bombardier, by adjusting the crank 246, holds the rate station pipcoincident with the marker pip. At the proper time the bomb releasecontact points close and the bombs are automatically released.

I claim as my invention:

l. I n a position determining system foi` a craft wherein there is aradio repeater ground station for receiving and re-transmittingperiodically recurring radio pulses, craft borne equipmentthat'comprises a radio transmitter for transmitting said radio pulses tosaid ground station, means Lfor receiving said radio pulses afterretransmission from said ground-station, means for producing periodictiming pulses, said craft borne equipment further comprising a cathoderay iiidicator tube having a viewing screen, means for deiiecting thecathode ray along a time axis periodically to producea trace onr saidscreen said deflections having a definite time relation, with respect tothe timing pulses, means for causing said periodic timing pulses toproduce an index mark on said trace, means for causing saidretransmitted pulses to produce indications on said trace, acontinuously rotatable phase shifter unit for shifting the time oftransmission of said radio pulsesfrom said craft with respect to saidtiming pulses, said phase shifter unit comprising a plurality ofgoniometers having their rotors eff 3. Thefinvention according to claim1 wherein,

means is' provided for indicating as a function of the setting of thephase shifter unit the instant that a predetermined position of h i cbeen reached. t e mart han 4. In a position determining system for acraftl wherein there are two ground radio repeater stations rforreceiving and retransmitting,periodically recurring rate pul=esl anddrift pulses re s ec craft borne .equipment p twel'y ground stations,:specradio means for receiving said 4rate Iand drift pulses afterretransmission.,l fromsaid ground stations, means for producing periodictiming pulses, said craft borne equipment funther comprising a cathoderay indicator tube having a viewing screen, means for deflecting thecathode ray along a time axis periodically'to produce a trace on saidscreen, said deflectionshaving a definite time relation with respect tothe timing pulses, means for causing said periodic timing pulses toproduce an index mark on said trace, means for causing said receivedrate and vdrifv4 pulses to produce indications on said trace, lacontinuously rotatable phase shifter unit for shifting the time oftransmission of said rate pulses from said craft with respect to saidtiming pulses, said phase shifter unit comprising a plurality ofgoniometers having their rotors effectively coupled to each other sothat they rotate at different speeds, and means for continuouslyrotating the rate-pulse phase shifter unit whereby the indicationproduced by the retransmitted rate pulses may be caused to remaincoincident with said index mark as the craft moves away from or towardthe rate-pulse ground station.

5. In a position determining system for a craft, radio equipment on saidcraft for transmitting radio pulses to a ground station and forreceiving said pulses after retransmission by said ground station,additional equipment on said craft which comprises a master oscillatorhaving an output signal of constant frequency, a chain of frequencydividers connected to said oscillator for supplying signals that havefrequencies which are submultiple frequencies of the oscillatorfrequency, a cathode ray indicator tube having a viewing screen, meansfor deflecting the cathode ray of said tube along a time axis insynchronism with a selected one of said submultiple frequency signals toproduce a trace on said screen, means for producing submultiple pulsesfrom said multiple frequency signals, respectively, pulse selectormeans, means for supplying to said selector means said oscillator outputsignal and said submultiple frequency pulses for selecting fractionalcycle pulses from said oscillator output signal which recur at thelowest submultiple frequency, means for causing said selected pulses toproduce index mark indications on said cathode ray trace, means forcausing the pulses received from said ground station to produceindications on said trace, a continuously rotatable phase shifter unitfor shifting the time of transmission of said radio pulses from saidcraft with respect to said timing pulses, said phase shifter unitcomprising a plurality of goniometers to which said oscillator outputand said submultiple frequency signals are applied, respectively, saidgoniometers having their rotors geared to each other with the gear ratiobetween successive rotors proportional to the frequencies of the signalsapplied to the goniometers, respectively, means for continuouslyrotating the phase shifter unit whereby the indication produced by theretransmitted radio pulses may be caused to remain coincident with saidindex mark as the craft moves away from or toward said ground station.

6. In a position determining system for a craft, radio equipment on saidcraft for transmitting radio pulses to a ground station and forreceiving said pulses after retransmission by said ground station,additional equipment on said craft which comprises a master oscillatorfor supplying an output signal, a chain of frequency dividers connectedto said oscillator for supplying signals that have frequencies which aresubmultiple frequencies of the oscillator frequency, a cathode rayindicator tube having., a viewing screen, means for deiiecting thecathode ray of said tube along a time axis in synchronism with aselected one of said submultiple frequency signals to produce a trace onsaid screen, means for producing timing pulses, means for causing saidtiming pulses to produce index mark indications on said cathode raytrace, means for causing the pulses received from said ground station toproduce indications on said trace, a continuously rotatable phaseshifter unit for shifting the time of transmission of said radio pulsesfrom said craft with respect to said timing pulses. said phase shifterunit comprising a` plurality of goniometers to which said oscillatoroutput signal and said submultiple frequency signals are applied, saidgoniometers having their rotors geared to each other with the gear ratiobetween successive rotors proportional to the frequencies of the signalsapplied to the goniometers, means for producing submultiple pulses fromsaid submultiple frequency signals, respectively, after they have passedthrough said goniometers, pulse selector means, means for supplying tosaid selector means said oscillator output signal and said submultiplefrequency pulses for selecting fractional cycle pulses from saidoscillator output signal for utilization as modulating pulses forproducing the radio pulses transmitted from the craft, and means wherebythe phase shifter unit may be continuously rotated for keeping theindication produced by the retransmitted rate pulses coincident withsaid index mark as the craft moves away from or toward the groundstation.

7. In a position determining system for a craft, radio equipment on saidcraft for transmitting radio pulses to a ground station and forreceiving said pulses after retransmission by said ground station,additional equipment on said craft which comprises a master oscillatorhaving an output signal of constant frequency, a chain of frequencydividers connected to said oscillator for supplying signals that havefrequencies which are submultiple frequencies of the oscillatorfrequency, a cathode ray indicator tube having a viewing screen, meansfor deflecting the cathode ray of said tube along a time axis insynchronism with a selected one of said submultiple frequency signals toproduce a trace on said screen, means for producing submultiplefrequency pulses for utilization as timing pulses, means for causingsaid timing pulses to produce index mark indications on said cathode raytrace, means for causing the retransmitted pulses received from saidground station to produce indications on said trace, means including acontinuously rotatable phase shifter unit for shifting the time oftransmission of said radio pulses from said craft with respect to saidtiming pulses, said phase shifter unit comprising a plurality ofgoniometers to which said oscillator output signal and said submultiplefrequency signals are applied, respectively, said goniometers havingtheir rotors geared to each other with the gear ratio between successiverotors proportional to the frequencies of the signals applied to thegoniometers, re-

` spectively, a modulating-pulse selector means,

means for producing submultiple pulses from the submultiple frequencysignals after they have passed through said goniometers, respectively,means for supplying to said modulating-pulse selector means saidlast-mentioned submultiple frequency pulses and also said oscillatoroutput signal after it has passed through one of said goniometerswhereby fractional cycle pulses from said oscillator. output signal areselected for utilization as said modulating pulses the timing of whichdepends upon the adjustment of said phase shifter unit, said modulatingpulses being supplied to the craft borne radio transmitter` fortransmission to the ground station as said radio pulses, and meanswhereby the phase shifter unit may be continuously rotated for keepingthe indication produced by the retransmitted radio pulses coincidentwith said index mark as the craft moves away from or toward said groundstation. .a

8. In a position determining system for a craft, radio equipment on saidcraft for transmitting radio pulses to a ground station and forreceiving said pulses after retransmission by said ground station,additional equipment on said craft which comprises a master oscillatorhaving an output signal of constant frequency, a chain of frequencydividers connected to said oscillator for supplying signals that havefrequencies which are submultiple 'frequencies of the oscillatorfrequency, a cathode ray indicator tube having a, viewing screen, meansfor deiiecting the cathode ray of said tubealong a time axis insynchronism with a selected one of said submultiple frequency signals toproduce a trace on said screen, means for producing submultiple pulsesfrom said multiple frequency signals, respectively, a timing-pulseselector means, means for supplying to said timing-pulse selector meanssaid oscillator output signal and said submultiple frequency pulses forselecting fractional cycle pulses from, said oscillator output signalfor utilization as timing pulses, means for causing said timingpulses toproduce index mark indications on said cathode ray trace', means forcausing the retransmitted pulses received from said ground station toproduce indications on said trace, means including a continuouslyrotatable phase shifter unit for shifting the time of transmission ofsaid radio pulses from said craft with respect to said timing pulses,said phase shifter unit comprising a plurality of goniometers to whichsaid oscillator output signal and said submultiple frequency signals areapplied, respectively, said goniometers having their rotors geared toeach otherwith the gear ratio between successive rotors proportional tothe frequencies of the signals applied to the goniometers, respectively,a, modulating-pulse selector means, means for producing additionalsubmultiple pulses from the submultiple frequency signals after theyhave passed through said goniometers, respectively, means for supplyingto said modulating-pulse selector means said additional submultiplefrequency pulses and also said oscillator output signal after it haspassed through one of said goniometers whereby fractional cycle pulsesfrom said oscillator output signal are selected for utilization as saidmodulating pulses the timing of which depends upon the adjustment ofsaid phase shifter unit, said modulating pulses being suppliedto thecraft borne radio transmitter for transmission to the ground station assaid radio pulses, and means whereby the phase shifter unit may becontinuously rotated for keeping the indication produced by theretransmittedradio pulses coincident with said index mark asl the craftmoves away from or toward said ground station.

9. The invention according to claim 8 wherein means is provided forinterrupting the operation of said chain of frequency dividers at aperiodic rate.

10. The invention according to claim 8 wherein periodic radio pulses aretransmitted alternately to rate and drift ground stations and whereinthe operation of said chain of frequency dividers is interrupted betweenthe periods of said transmissions to said rate and driftgroundvstations. y

11. In a position determining system Afor a craft wherein there are twoground radio repeater stations for receiving and retransmitting l 8periodically recurring rate pulses and drift pulses,

respectively, craft borne equipment that com` prises a radiotransmitterfor transmitting said rate pulses and said drift pulses to said groundstations. respectively, means for receiving said rate and drift pulsesafter retransmission from said ground stations, means for producinglpe.-

riodic timing pulses, said craft-borne equipment further comprising'acathode ray indicator tube having a viewing screen, means for deilecting`the cathode ray along a time axis periodically said trace, continuouslyrotatable phase shifter units for shifting -the time of transmission ofsaid rate vand drift pulses, respectively, from said craft with respectto said timing pulses,

motor driving means for continuously rotating the rate-pulsephaseshifter unit, and means for adjusting the vrate at which said drivingmeans rotates said rate-pulse phase shifter unit whereby the indicationproduced by the retransmitted rate pulses may' be caused to remaincoincident with said index mark as the craft moves away from or towardthe pulse-rate ground station.

12. Inv a position determining system for a craft wherein there are twoground radio repeater stations for receiving rate pulses and dri-ftpulses, respectively, craft-borne equipment that comprises a radiotransmitter for transmitting said rate pulses and said drift pulses tosaid ground stations, means on said craft for receiving said rate anddrift pulses after retransmission from said ground stations, saidcraft-borne equipment further comprising a cathode ray indicator tubeand means .for producing a time sweep thereon, means for producing aperiodic timing pulse vthat appears on said sweep as an index mark,means for causing said received rate and drift pulses to appear on saidsweep, continuously rotatable phase shifter units for shifting the timeof transmission from the craft of said rate and drift pulses, repectively, a computer which includes a motor f iving'means, means forcoupling said rate-puls phase shifter means to rsaid driving means forlcontinuously rotating said phase shifter, and means for adjusting therate at which said driving means rotates said rate-pulse phase shifterunit whereby a received rate pulse indication may be caused to remaincoincident with said index mark as the craft moves away from or towardthe rate-.pulse ground station and whereby the rate of travel' of saidcraft away from or toward said ratepulse ground station is fed into saidcomputer.

13.- In a position determining system for a craft wherein there are twoground radio repeater stations for receiving and retransmitting rateplses and drift pulses, respectively, craft-borne equipment thatcomprises a radio transmitter for` and drift pulses after retransmissionfrom said ground stations, said' craft equipment further comprising acathode ray indicator tube and means for producing a time sweep thereon,

means for producing periodic timing pulses that appear on said sweep toproduce an index mark,v

means for causing said received -rate and drift pulses toappear on saidsweep, continuously roground station and whereby the rate of travel 0fsaid craft away from or toward saidrate-pulse ground station is fed intosaid computensaid computer further including a bomb-release contactpoint and means for moving it towardits bomb-release position at a ratethat is a function of the rate at which said rate pulse phase shifterunit is rotatedand means for changing the position of said contact pointwith respect to its bomb-release position in response to an adjustmentof the rate at which said rate-pulse phase shifter unit is driven.

14. In a position determining system for a craft wherein radio equipmenton said craft transmits radio pulses to a ground station and receivessaid pulses after retransmission by said ground station, additionalenuipment on saidcraft v-hch comprises an oscillator for supplying anoutput signal, a chain of frequency dividers connected to saidoscillator for supplying signals that have frequencies which aresubmulfiple frequencies of the oscillator frequency, a cathode rayindicator tube having a viewing screen, means for deflecting the cathoderay of said tube along a time axis in synchronism with a selected one ofsaid signals to produce a trace on said screen, means for producingsubmultiple pulses from said submultiole frequency signals,respectively, pulse selector means, means for supplying to said selectormeans seid oscillator output signal and said subrnultiple frequencypulses for selecting fractional cycle pvlses from said oscillator outputsignal, said selected fractional cycle pulses recurring at therepetition rate of the lowest frequency submultiple freqrency pulses,means for causing said selected pulses to produce index mark indicationson said caihode ray trace, and means for interrupting ataa periodic ratethe operation of said frequency divider chain.

15. In receiving apparatus for indicating the timing of signal pulseswith respect to timing pu1sessaid signal pulses being transmitted from apoint remote from said receiving apparatus, a. cathode ray indicatortube having a viewing screen, means at said receiving apparatus forproducing timing pulses recurring at a predetermined repetition rate,means for deecting thev cathode ray of said tube along a time axis at apulse-repetition rate to produce a plurality of superimposed traces onsaid screen, means for f causing one of said signal pulses to produce asignal indication pip on one of said traces during one sweep of thecathode ray along the time axis,

and means for causing one of said timing pulses to produce an indexindication` pip on another of said traces during a successive sweep ofsaid cathode ray along the time axis and before the next signal pulseoccurs whereby said two pips may be superimposed without adding to eachother to produce a single pip instead of the desired two separate pips.

16. In receiving apparatus for indicating the timing of signal pulseswith respect to jtiming pulses, said signal pulses being transmittedfrom a point remote from said receiving apparatus, a cathode rayindicator tube having a viewing screen, means at said receivingapparatus for producing timing pulses'recurring at a predeterminedrepetition rate, means for deflecting the cathode ray of said tube alonga time axis at as repetition rate that is a multiple of said timingpulse repetition rate to produce a.k plurality of superimposed traces onsaid screen in the absence ing one sweep of the cathode ray along thetime,V

axis, means for causing one of said timing pulses to produce an indexindication pippnanother of said traces during a successive sweep of saidcathode" ray along the time axis and before the next signal ypulseoccurs whereby said two pips may be adjusted to the position ofcoincidence and still remain as two separate pips, and means forblanking all of the cathode ray sweeps except said two sweeps on whichsaid signal and index pips appear. l

17. In a position determining system for a craft. radio equipment onsaid craft forl transmitting radio pulses to a ground station and forreceiving said pulses after retransmission by said ground station,additional equipmenton said craft which comprises an oscillator forsupplying an output signal, a chain of frequency dividers connected tosaid oscillator for supplying signals that have frequencies which aresvbmultiple frequencies of the oscillator frequency, a cathode rayindicatortube having a Vviewing screen, means for deflecting the cathoderay of said tube along a time axis in synchronism with a selected one ofsaid submultiple frequency signals to produce a trace on said screen,means for maintaining said indicator tube biased to cathode-ray cut-offin the absence of applied sgnals, means for producing timing pulses,means for causing said timingr pulses and the pulses received from saidground station to produce an index mark indication and a signalindication, respectively, on the traces produced by different successivedeflections of the cathode ray, means for unblanking saidcathode rayduring said diierent successive deflections only, and a continuouslyrotatable phase shifter unit for shifting the4 time of transmission ofsaid radio pulses from said craft with respect to said timing pulses.

18. In a position determining system for a. craft, radio equipment onsaid craft for transmitting radici pulses to a ground station and forreceiving said pulses after retransmission by said ground station,additional equipment on said craft which comprises an oscillator forsupplying an output signal, a chain of frequency dividers connected tosaid oscillatorl for supplying signals that have frequencies which aresubmultiple frequencies of the oscillator frequency, a cathode rayindicator tube having a viewing screen, means for deilecting the cathoderay of said tube along a time axis in synchrnism with a selected one ofsaid submultiple frequency signals to produce a .trace on said screen,means for maintaining said indicator tube biased to cathode-ray cut-offin the absence of applied signals, means for producing timing pulses,means for causing said timing pulses and the pulses received from saidground station to produce an index mark indication and a signalindication, respectively, on the traces produced by different successivedeflections of the cathode ray, means for unblanking said cathode rayduring said different successive deflectionsonly,

a continuously rotatable phase shifter unit for shifting the time oftransmission of said radio successiverotors proportional to thefrequencies' of the signals applied tothe goniometers, means forproducing submultiple pulses from said submultiple frequency signals,Irespectively, after they have passed through said goniometers,

pulse selector means, means for supplying to said selector means saidoscillator output and said submultiple frequency pulses for selectingfractional cycle pulses from said oscillator output signal forutilization as modulating pulses for producing the radio pulsestransmitted from the craft, and means whereby the phase shifter unit maybe continuously rotated for keeping the indication produced by theretransmitted rate pulses coincident with said index mark as the craftmoves away from or toward the ground station.

19. In a position determining system for a craft, radio equipment onsaid craft for transmitting radio pulses to a ground station and forreceiving said pulses after retransmission by said ground station,additional equipment on said craft which comprises a master oscillatorfor supplying an output signal, a chain of frequency dividers connectedto said oscillator for supplying signals that have frequencies which aresubmultiple frequencies of the oscillator frequency, a cathode rayindicator tube having a viewing screen, means for deflecting the cathoderay of said tube along a time axis in synchronism with a selected one ofsaid submultiple frequency signals to produce a trace on said screen,means for producing submultiple pulses from said submultiple frequencysignals, respectively, means for producing a delayed submultiplefrequency pulse from the lowest submultiple frequency signal, atiming-pulse selector means, means for supplying to said timing-pulseselector means said oscillator output signal and said submultiplefrequency pulses for selecting fractional cycle pulses from saidoscillator output for utilization as timing pulses, said last meansincluding means for selectively applying to the selector either thedelayed or the undelayed lowest submultiple frequency pulse whereby aregular timing pulse or an offset timing pulse may be obtained, meansfor causing the selected timing pulse to produce an index markindication on a cathode ray trace, means for causing the retransmittedpulses received from said ground station to produce an indication onsaid trace, and means including a continuously rotatable phase shifterunit for shifting the time of transmission of said radio pulses fromsaid craft with respect to said timing pulses.

20. The invention according to claim 19 wherel in means is provided forbiasing said indicator tube to cathode-ray cut-off in the absence ofapplied signals and wherein means is provided for utilizing saidsubmultiple frequency pulses for unblanking the cathode ray during thereception of signal pulses and the occurrence of offset timing pulsesonly.

21. The invention according to claim 19 wherein means 1s provided forbiasing sala' malestar tubeto cathode-ray cut-off `in the absence ofapplied signals and wherein means is provided for utilizing alternatehigher frequency submultiple frequency pulses for unblankingl thecathode ray during the occurrence of received t:signlgl pulses andoffset` timing pulses, respec- 22. The invention according to claim 19wherein means is provided for biasing said indicator .tube tocathode-ray cut-offin the absence of applied signals and vwherein meansis providedv for utilizing said delayed and said undelayed lowestfrequency submultiple 'frequency pulses forunblanklng the cathode rayduring the occurrence of received signal pulses 'and oflfset` timingpulses, respectively.

23. In a position determining system for a craft. radio equipment onsaid craft for transmitting radio pulses to a ground station and forreceiving said pulses after retransmission'by said ground station,Vadditional equipment on said craft which comprises a master oscillatorfor supplying an output signal. a chain of frequency dividers connectedto said oscillator for supplying signals that have frequencies which aresubmultiple frequencies of the oscillator frequency,v

a cathode .ray indicator tube having a viewing screen, means fordeflecting the cathode ray of said tube along a time axis in synchronismwith a selected one; of said submultiple frequency signals to produce atrace on said screen, means for maintaining said indicator tube biasedto s cathode-ray cut-off ink the absence of applied signals, means forproducing submultiple pulses from said submultiple frequency signals,respectively, means for producing a delayed submultiple frequency pulsefrom the lowest submultiple frequency signal, a timing-pulse selectormeans, means for supplying to said timing-pulse selector means saidoscillator output signal and said submultiple frequency pulses forselecting fractional cycle pulses from said oscillator output forutilization as timing pulses, said last means including means forselectively applying tothe selector either the delayed or the undelayedlowest submultiple frequency pulse whereby a regular timing pulse or anoffset timing pulse may be obtained, means for causing the selectedtiming pulse to produce an index'mark indication on a cathode ray trace,means for causing the retransmitted pulses received from said groundstation to produce an indicationl on said trace, a circle-lighting pulseselector means, means for supplying the highest frequency submultiplefrequency pulses to said last selector means, means for supplying boththe delayed and the undelayed lowest frequency submultiple frequencypulse to said last selector means for selecting two of said highestfrequency submultiple frequency pulses, means for utilizing said lasttwo pulses for unblanking the cathode ray, and means including acontinuously rotatable phase shifter unit for shifting the time oftransmission of said radio pulses from said craft with respect to saidtiming pulses.

24. In a position determining system for a craft, radio equipment onsaid craft for transmitting radio pulses to a ground station and forreceiving said pulses after retransmission by said ground station,additional equipment on said craft which comprises a master oscillatorfor supplying an output signal, a chain of frequency dividers connectedto said oscillator for supplying signals that have frequencies which aresub- 23 multiple -frequencies oi' the oscillator frequency, a cathoderay indicator tube having a `viewing screen, means for deflecting thecathode ray of said tube along a time axis in synchronism with aselected one of said submultiple frequency signals to produce a trace onsaid screen, means for producing submultiple pulses from saidsubmultiple frequency signals, respectively, means for producing adelayed submultiple frequency pulse from the lowest submultiplefrequency signal, a timing-pulse selector means, means for supplying tosaid timing-pulse selector means said oscillator output signal and saidsubmultiple frequency pulses for selecting fractional cycle pulses fromsaid oscillator output for utilization as timing pulses, said last meansincluding means for selectively applying to the selector either thedelayed or the undelayed lowest submultiple frequency pulse whereby aregular timing pulse or an offset timing pulse may be obtained, meansfor causing the selected timing pulse to produce an index marklndicationon a cathode ray trace, means for causing the retransmitted pulsesreceived from said ground station to produce an indication on saidtrace, means including a, continuously rotatable phase shifter unit forshifting the time of transmission of said radio pulses from said craftwith respect to said timing pulses,

said phase shifter unit comprising a plurality oi' means for producingadditional submultiple pulses from themultiple frequency signals afterthey have passed through said goniometers, respectively, means forvsupplying to said modulating-puise selector `means said additional sub,-multiple frequency pulses and said oscillator output signal after it haspassed through one `of said goniometers for selecting fractional cyclepulses from said oscillator output for utilization as said modulatingpulses, the timing of vsaid modulating pulses depending upon the adjustment of said phase shifter unit, said modulating pulses being suppliedto the craft borne radio transmitter for transmission to the groundstation as said radio pulses, and means for continuously rotating thephase shifter unit whereby the indication produced by the retransmittedradio pulses may be caused to remain coincident with said index mark asthe craft moves away from or toward said ground station.

STUART W. SEELEY.

REFERENCES `CITEDV The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Hayes Oct. 14, 1947

